Surface Engineering Enables Efficient AgBiS<sub>2</sub> Quantum Dot Solar Cells

Surface\nligand chemistry is vital to control the synthesis, diminish\nsurface defects, and improve the electronic coupling of quantum dots\n(QDs) toward emerging applications in optoelectronic devices. Here,\nwe successfully develop highly homogeneous and dispersed AgBiS<sub>2</sub> QDs, focus on the control of interdot spacing, and substitute\nthe long-chain ligands with ammonium iodide in solution. This results\nin improved electronic coupling of AgBiS<sub>2</sub> QDs with excellent\nsurface passivation, which greatly facilitates carrier transport\nwithin the QD films. Based on the stable AgBiS<sub>2</sub> QD dispersion\nwith the optimal ligand state, a homogeneous and densely packed QD\nfilm is prepared by a facile one-step coating process, delivering\na champion power conversion efficiency of approximately 8% in the\nQD solar cells with outstanding shelf life stability. The proposed\nsurface engineering strategy holds the potential to become a universal\npreprocessing step in the realm of high-performance QD optoelectronic\ndevices.